Thin film resonators having a diaphragm consisting of a piezoelectric zinc oxide film on a silicon or silicon dioxide film are generally known and have received considerable attention due to the fact that such devices exhibit a low temperature coefficient at the resonant frequency which is determined by the thickness of the piezoelectric film. Resonant frequencies in the VHF/UHF frequency range have been developed and have received considerable attention inasmuch as these devices are compatible with integrated circuit structures in their fabrication processes and device size. Further, a self-supported thin film resonator with a very thin air-gap between the semiconductor surface and the diaphragm bottom surface has been developed and is disclosed, for example, in a publication entitled "Air-Gap Type Piezoelectric Composite Thin Film Resonator", H. Satoh et al, Proceedings of the 39th Annual Symposium On Frequency Control, 1985, pp. 361-366. While such resonators are presumed to operate as intended, certain inherent limitations nevertheless exist, particularly as it relates to their fabrication.
It is an object of the present invention, therefore, to provide an improvement in piezoelectric resonators.
It is a further object of the invention to provide an improvement in thin film piezoelectric resonators.
It is still another object of the invention to provide an improvement in air-gap type piezoelectric thin film resonators and their relative ease of fabrication so as to provide a higher device and circuit yield.
It is still yet another object of the invention to apply an improvement in air-gap type thin film resonators having a cantilever construction to implement a monolithic chemical sensor.